achieve test run objectives with advance preparation and real … · achieve test run objectives...

Achieve Test Run Objectives with Advance Preparation and Real Time Reports

Charles D. Herzog, PE

Consulting (Retired) Chemical Engineer

Herzog Process Services, PLLC

AIChE South Texas Section, Jan 2019

HERZOG PROCESS SERVICES, PLLC


• Performance guarantee

• Root cause analysis

• Scope identification for revamp project

• Others?

Types of Test Runs


• Confirm material balance envelope

• Prepare Excel calcs and reports in advance

• Obtain or create a simulation of the system

• Verify DCS data acquisition / migration to Excel

• Synchronize lab data with DCS data

• Make a plan to reconcile data into a balance

Test Run Preparation

Material Balance Envelope for Crude Oil Unit


Charge Pump

Furnace

PreFlash

Desalter

Crude Tower

BS&W (un-measured)

Gas

LSR

AGO

Dist

Nap

GasInclude Tag Numbers for All

Lines Crossing Envelope

Confirm Material Balance Envelope

• Use daily material balance calcs as a starting point

• Normally closed lines must be included

• Agree how to account for any flaring during the test

• Identify any un-measured lines crossing envelope

• Try to use single-phase lines for flow measurement

• Confirm material balance closure prior to test


Orifice Meters Work Best with One-Phase Flow


FI

TI

Cooler

Flash Drum

This section of pipe may contain

2-phase flow

Flow Data is Reconciled Against Tank Volume


DistillateProd Pump

Crude Tower

Distillate Tank

FILI

Tank Does Not Have to be Inactive for Entire Test Period

Distillate Stripper

‘Strapping Tables’ provide net liquid volume at any level

TI

Downstream Data Reconciles Product Rate


DistillateProd Pump

Crude Tower

Distillate HydroTreater

FI FI

Feed meter at DHTconfirms product rate

Distillate Stripper

TI TI

Confirm Envelope with Downstream Unit


DistillateProd Pump

Crude Tower


FI FI

This method works best when a third

meter is not involved

Distillate Stripper

To Unit BFI

Confirm Envelope with Downstream Unit


DistillateProd Pump

Crude Tower


FI FI

This method works best when a third

meter is not involved

Distillate Stripper

To Unit B

FI

Identify Problems BEFORE Test Begins


Gas OilPump

Crude Tower

Gas Oil Tank

FI

LI

Real Example:Product Flowmeter Inside

Recycle Loop – Caused 75% Error in Flow

NCProblem was identified

before test because of poor material balance closure

Refrigeration Example: Simulation Helps!

Level Must be Steady to Reconcile Data

Use Chiller Data Sheet and Condensing Curve


FI

FI

TI

Saturated HCVapor Feed

LC

Chiller

Refrigerant Vapor

Refrigerant Liquid

FI

FI

Sources of Flaring During Test

• Venting of non-condensibles from exchangers

• Exceeding capacity of condensing heat exchanger

• Making off-spec product

• Increasing the feed too rapidly can result in flaring



• Control system may fail to keep unit steady

• Equipment constraints may cause adverse result

What Happens if Feed Increases too Rapidly?

Reduce Pressure Variation to Reduce Flaring


TIME

LIMIT

TIME

LIMIT

Initial SP

PR

ESSU

RE

PR

ESSU

RE

PC SETPT

PC SETPT

Condenser Constraint Causes Test Failure


Liquid Feed

CW

STM

VENT

98% SPEC

HEAVY RECYCLE

REFLUX

FC

PC

AIAI LC

LC

TC

Synchronize Lab Data with DCS Data

1. Create a ‘Lab Data’ page on the Operator console

2. List all samples to be taken during the test

3. Operator clicks ‘Sample Caught’ as sample is drawn

4. Lab results are correctly saved in test historian


Synchronize Lab Data with DCS Data

Typical ‘Lab Data’ Entry Page

Date: xx Time: yy

Crude Oil

Naphtha Sample

Kerosene Caught

Gas Oil

Operator uses this display to time-stamp Kerosene sample


Obtain or Create a Simulation of the System

• Often there is an existing simulation available

• Use simulators for balances and density calculations

• Simulation can help identify certain problems

• Simulating the system adds credibility

• Agreed simulation leads to report acceptance


Use Simulation to Identify Root Cause


REFRIGERANT LIQUID

REFRIGERANT VAPOR

Refrigerated exchangers unable to provide enough

cooling for max rates

Non-condensiblesreduce refrigerant

partial pressure

Operators reduce suction pressure to

get extra cooling

TWO-PHASEREFRIGERANT

TIPI

TI

Simulation cannot find equilibrium

P and T that match


• Verify material balance closure in advance

• Bring plant to test run conditions SLOWLY

• Get products on spec before increasing feed

• Ensure levels are steady before increasing feed

• Provide real-time feedback to Operations

• Identify equipment nearing its capacity limit

On Site Test Activities

Test Run Spreadsheet


Use spreadsheet for most functions:

• Data Acquisition / Flow Compensation

• Heat and material balancing

• Management reports

• Saving intermediate results of all complex calcs

Test Run Spreadsheet


• Only the spreadsheet ‘Owner’ changes formulas

• Owner provides data entry areas as necessary

• Exercise care in copying and pasting formulas

• Naming cells or ranges eliminates some errors

Data Acquisition


Establish a single data acquisition sheet for raw data

• Create a data block for every flowmeter in the system

• Include columns for temp, press, and compensation calcs

• Verify instrument ranges from latest instrument data sheets

• Include all related tags in the data acquisition list

• Include ‘redundant’ tags at upstream or downstream units

Typical Data Block


Tag: FI-1000 Desc: Ethylene Product Units: Mlb/hr

Flow: 120.0 Oper P: 1800 psi Oper T: 60° F Dens: 24.0 lb/cf

Time Raw Flow Press Temp Dens Factor Comp Flow

0100 112.0 1820 58.2 24.1 1.002 112.2

0115 112.2 1819 58.1 24.1 1.002 112.4

0130 112.3 1819 58.1 24.1 1.002 112.5

Simulator calculates densityfor compressible fluids

Ensure continuity withreference density

Consider Using a Tool to Create Data Blocks


Process Liquid

Condensate

Steam

Process Gas

Add New Process Liquid Tag

Flow Compensation Type

Base Gravity Measurement

Flow Gravity Measurement

Temperature Tag

Gravity Tag

Full Scale Flow Mlb / hr

Base Gravity or Density lb / cu ft

° F

lb / cu ft

none

ti-1

gi-1

100.00

Gravity Units

50.00

Design Temperature

49.00Grav / Dens at Design Temp

fi-1

overhead

lb

hr

lb / cu ft

Liq Mass

not measured

90.00

Tag Name

Description

Flow Units

Time Units

Establish Flow Compensation


• Engineering units may be mass, volume, or std volume

• Flow compensation equation depends on units of flow

• Create columns for each flow tag:• “Raw” flow from DCS

• Compensating temperature

• Compensating pressure

• Molecular weight (based on analysis)

• Flowing gravity for liquids

• Compensated flow

Orifice Flow Meter Compensation


• Based on Bernoulli’s Principle

• Typical orifice measures differential pressure (ΔP)

• Mass flow proportional to ( ΔP x ρ ) ½

• Flow meter compensation accounts for density

• L.K. Spink is a reference for flow compensation

ΔP

Frequently Used Compensation Equations


Vapor Streams:

• P, T, MW compensation for compressibility > 0.9

• Typical Eng Units are Mass or ‘Standard Vapor Volume’

Liquid Streams:

• Liquid density independent of pressure

• Estimate slope of density vs temperature

• Standard volume (e.g., barrels) use different equations

Use GPSA Tables for Oil Products


GPSA Fig 23-10

Gravity vs Temp

Standard Vapor Comp vs Mass Flow Comp


Examples of Standard Vapor Flow Units:

• Standard Cubic Feet Per Minute (SCFM)

• Normal Cubic Meters Per Hour

Standard Vapor Flow is Proportional to MOLES / HR

Standard Vapor Comp vs Mass Flow Comp


Vapor Mass Flow Compensation:

Comp Factor = ( P/P0 x T0/T x MW/MW0 ) 1/2

Standard Vapor Flow Compensation:

Comp Factor = ( P/P0 x T0/T x MW0 /MW) 1/2

Standard Liquid Comp vs Mass Flow Comp


Example of Standard Liquid Flow Units:

Standard Barrels Per Day (BPD)

Standard Barrels are Referenced to ‘Base Gravity’

Base Gravity = GB = Specific Gravity at 60°F

The base gravity is a function of composition only

Standard Liquid Comp vs Mass Flow Comp


Mass Flow Compensation:

Comp Factor = ( ρ / ρ0 ) 1/2

ρ = ρ0 + slope x (T - T0 )

Standard Liquid Flow Compensation:

Comp Factor = ( GF / GF0) 1/2 / (GB0 / GB)

GF and GF0 refer to flowing specific gravity at T and T0

Common Problems to Avoid


• Allowing insufficient time to prepare

• Using the incorrect flow compensations

• Failure to review report with Operations

• Failure to verify balances before test

• Failure to tune DCS control loops

Create a Tool for Operations Staff


• Establish flexible test run report with user-entered

start and end times

• Having a computer-savvy person on the team helps

• Make certain that operations staff understand report

format and calculations before actual test begins

Test Run Report for Crude Oil Unit


Date: xx Time Start: yy Time End: zz

Overall Test Last 4 Hours

Feeds: MB/D LB/HR MB/D LB/HR Crude A aa bb cc dd

Crude B etc

Total

Products......

Total

% Error

Include Tag Numbers for All Streams

Final Test Preparations


• Review unit operation for 24 hours prior to test

• Ensure that the unit material balance is reaching acceptable closure

• Identify any unsteady flows or operating conditions. Fix control problems if possible

• Control problems tend to get worse when equipment operates near capacity limit

Offer Assistance During the Test


• Once the actual test has begun, be available to

offer assistance as needed.

• Monitor the initial reports during the first few

hours of the test.

• Identify any material balance errors or any

performance criteria that are not being satisfied.


Thank You!

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